CYCLOPALLADATED AZOBENZENE AND AZOXYBENZENE MONONUCLEAR COMPLEXES

A number of cyclopalladated mononuclear species, viz. [(Azoxy-6)Pd(che late)], [(Azo-6)Pd(chelate)] and [(Azo-6, CO8)Pd(chelate)], have been assembled through a multistep synthesis starting from a Pd(II) source, the mesogens 4,4'-bis(hexyloxy)azoxybenzene, H(Azoxy-6) [solid (room temperature) --> nematic (80 degrees C) --> isotropic liquid (126 degr ees C)], 4,4'-bis(hexyloxy)azobenzene, H(Azo-6) [solid (room temperatu re) --> nematic (104 degrees C) --> isotropic liquid (116 degrees C)], or 4-hexyloxy-4'-[(4 ''-octyloxy)benzoyloxyl]azobenzene, H(Azo-6, CO8 ) [solid (room temperature) --> nematic (108 degrees C) --> isotropic liquid (211 degrees C)], and the potentially chelating O,O monoanionic ligands 2,4-pentanedionate (acac), 1,1,1,5,5,5-hexafluoro-2,4-pentane dionate (hfacac) and tropolonate (trop). The O,N ligands, 2-aminopheno late (2-aph) and 2-amino-2-methyl-1-propanolate (2-apr) have been also reacted with H(Azoxy-6) and H(Azo-6). All the new synthesized mononuc lear species have an asymmetric molecular shape as the previously inve stigated [(Azoxy-6)Pd(acac)] and were expected to present thermotropic mesomorphism alike. Nevertheless, only the [(Azo-6, CO8)Pd(O,O)] comp ounds are nematic liquid crystals.